Diamond grinding of glass



April 1955 c. w. HIGHBERG DIAMOND GRINDING OF GLASS 6 Sheets-Sheet 3Original Filed Aug. 18. 1960 FIG. 5

l hmzomuzzv 56 58.2% a20 5 O o 0 II l2 I3 NO.I234567 w m m Q w c m. D NO I M I x mm m m 5 M m V D IBM l L 65 5mm L W R w m M m m m o o o m O.O. O. 0 0 O Ifimzuzo wo hw\ o 2wm wmjo r O 0 0 0 0 O 6 5 4 3 2 lINVENTOR.

CARLE W. HIGHBERG BY 3 ATTORNEY April 13, 1965 c. w. HIGHBERG 3,177,624

DIAMOND GRINDING OF GLASS Original Filed Aug. 18. 1960 6 Sheets-Sheet 4o a a l. o o 0 o D o 0 H I Q... SN I 3 Tw m D OH S N so=| COOLANTCONCENTRATION FIG. 8

l PowErS/" WHEEL LIFE O0 O0 62 22 u u] JuuI;

INVENTOR. CARLE W.HIGHBERG BY W J ATTORNEY I5 20 I DIAMOND CONCENTRATION(cARATs/m?)- A ril 13, 1965 c. w. HIGHBERG DIAMOND GRINDING OF GLASS 6Sheets-Sheet 5 Original Filed Aug. 18. 1960 INVENTOR."

CARLE w. HIGHBERG BY j ATTORNEY April 1965 c. w. HIGHBERG DIAMONDGRINDING OF GLASS 6 Sheets-Sheet 6 Original Filed Aug. 18. 1960 FIG."

FIG. I3

FIG. l4

FIG. l2

NVENTOR CARLE W. HIGHBERG ATTORNEY United States Patent 3,177,624DEAMQND GRHNDENG 6F GLAS Carle W. Highherg, Murray Hill, NJ, assignor toEngelhard Hanovia, inc, Newark, Ni, a corporation of New Jersey Originalapplication Aug. 18, 1960, Ser. No. 50,352. Divided and this application.luiy 18, 1951, Ser. No.

4 (liaims. (Cl. 51ll10) This invention relates to glass grinding, andmore particularly to the grinding of glass with diamond grinding wheels.

This application is a division of application Serial No. 50,352, filedAugust 18, 1960, now abandoned.

In accordance with present day techniques for manufacturing plate glass,the plate glass surface is processed at each of a very large number ofsuccessive grinding and polishing stations spaced along a conveyor line.In one typical installation, glass sheet having a width of 96 inches iscontinuously extruded from a melting furnace. Following passage throughan annealing chamber, the plate glass is passed through 28 successivebeach sand grinding stations. At each of these stations, the grindingoperation is accomplished by large grinding heads having verticallymounted spindles, which have horizontal grinding surfaces extendingacross the 96 inch width of the plate glass. Following the 28 beach sandgrinding stations, 42 additional polishing stations are required. Thepolishing heads also have vertical spindles, and rouge or iron oxide isemployed as an abrasive.

The conveyor rate for the known process is between 170 and 180 inchesper minute, and the total glass re moved is about 0.025 inch. Thesurface finish at the end of the beach sand grinding stages is about 16to 18 microinches, on a root mean square basis, and at the end of thepolishing operations, it is significantly less than one micro inchR.M.S. As noted above, to obtain these results 70 stations, eachincluding a rotary grinding wheel at least 96 inches in diameter, havebeen required for the surfacing or" one side of the glass sheet.

This prior art process for grinding plate glass has the obviousdisadvantage that a large amount of expensive machinery and floor spaceis required. Furthermore, the facilities and manpower required forhandling the bulky abrasives are very costly. It is, therefore, aprincipal object of this invention to reduce the amount of floor space,machinery, and materials handling expenses, required in the processingof plate glass, and to reduce the cost of the l entire operation.

In general, this may be accomplished by replacing twothirds or more ofthe seventy stages of grinding and polishing which are now being usedwith a lesser numher, such as fifteen or less, stages of diamondgrinding. With proper successive diamond grinding stages as describedbelow, great savings may be realized by eliminating many of the largenumber of stages which are now required in the processing of plateglass. Furthermore, it is interesting to note that, while diamonds arecommonly considered to be expensive, the actual cost of diamonds percubic inch of removed glass is actually less than the cost of the beachsand or rouge abrasives which are now in use.

In accordance with one important feature of the present invention, ithas been determined that the diamond concentration, in terms of caratsper cubic inch of grinding wheel matrix, should be relatively low in thecase of the initial heavy cuts of glass. More specifically, it has beendetermined that concentrations of less than twenty, and preferably aboutten carats per cubic inch are desirable for the initial cuts.

Patented Apr. 13, 1965 With regard to the heavy initial cuts, otherrepresentative specific operating conditions may typically include afeed speed of 200 inches per minute of the glass relative to thegrinding wheel, and a cut of about 0.006 or 0.004 inch. The grit sizemay be approximately the 50 to 60 grit size, having an average particlesize of about 275 microns. In this regard it is noted that larger gritsizes of the order of the 20 to 30 grit size tends to cause excessivechipping at the edges, and breakage of plate glass. The foregoingspecific data included in this paragraph indicates the orders ofmagnitude which are involved; broader ranges are set forth below in thepresent specification and claims.

in accordance with another feature of the invention, the concentrationof diamonds per cubic inch should be increased in successive grindingstages, with reduction in the depth of the cuts and also with thecorresponding reduction in diamond particle size.

In accordance with a further feature of the invention, a diamondgrinding wheel includes a generally circular support, and a large numberof diamond segments mounted to form a grinding plane extending generallyperpendicular to the axis of the support. The grinding surface of thesegments may be very small, and the segments may be adjustable toprovide various effective diamond grinding wheel widths, such that wheellife, or eiiiciency, may be extended for various grinding conditions.

When the method and arrangements described in the present specificationare followed, an unexpectedly high efficiency, or wheel life, in termsof removal of glass per carat of diamond, is achieved. In accordancewith the present invention, this wheel life is in the order of 2600 ormore cubic inches of glass removed per carat of diamond. With this longwheel life, in combination with the elimination of many stages ofprocessing as discussed above, the process of the present invention issignificantly more economical than prior processes.

Other objects, features and advantages of the present invention willbecome apparent from a consideration of the following detaileddescription and from the accompanying drawings, in which,

FIGS. 1 and 2 represent a single diamond grinding station for use inprocesses and systems of the present invention;

FIG. 3 represents a known plate glass finishing process;

.FIG. 4 is a diagram showing a process using diamond grinding andindicating the approximate number of stations which may be eliminated bythe use of the present diamond grinding inventions;

FIG. 5 is a set of plots showing certain details with regard to onespecific diamond grinding process, in accordance with the presentinvention;

FIG. 6 is a plot showing the relationship of diamond grinding wheel lifeto grinding head speed in surface feet per minute;

FIG. 7 includes two plots indicating the effect of coolant concentrationon wheel life for diamond grinding wheels;

FIG. 8 shows, in two plots, the effect of diamond concentration on wheellife and power;

FIGS. 9 and 10 are two views of a diamond wheel support member and theadditional elements required to support the diamond grinding segments,in accordance with this invention;

FIGS. 11 and 12 show the details of the segment holders, the diamondsegment mounts, and the individual diamond segments, which are assembledwith the support of FIGS. 9' and 10;

FIGS. 13 through 15 show the construction of the individual diamondsegments and their mounts;

FIG. 16 represents a portion of the grinding wheel support, particularlyindicating the tapped holes which may 'determined'principally by thespacing of the grinding whcel 18 "from the bed- 32 of the grindingstage. Under schematic showings of a grinding station in accordance Wwith the principles of the present invention. A sheet of plate glass 12is fed through the grindingstation by any suitable means such as thedriving rollers '14 through 17, as shown in FIG. 2. Alternatively, theglass may be blocked or clamped to a suitable supporting surface and maybe fed with its supporting member through the grinding stage. Thegrinding stage includes a generally circular diamond grinding wheel 18having a diameter greater than the width of the plate glass sheet 12.The grinding wheel 18 is mounted on a vertical spindle contained withinthe bearing housing as shown in FIG. 1.

. 4 normal circumstances, this rate of stock removal will range from aninitial cut of about 0.006 inch down to significantly less than 0.001inch at the final stages of diamond grinding. v

With regard to the diamond grinding material itself, a diamond grindingwheel is normally composed of small particles of diamond embedded in amatrix. The matrix a "is termed the bond. Diamond wheels for thegrinding The wheel is driven by a motor 22 which may be which alsosupports the bearing housing for the verof glass are normally made withmetal bonds. One typical bond which has proved satisfactory includesapproximately 60 percent copper, 24 percent'zinc, ll percentsilver-copper solder, with the silver making up two-thirds tothree-fourths of thesolder, about 2 percent of iron and 1 percent ofmanganese. Other bonds including copper and tin and various combinationsof the elements mentioned above, are also satisfactory. Steel bondedwheels may also be employed. Ingeneral, it is contemplated that a widevariety of bonds may be-employed.

With regard to-the diamond content in the abrasive materiah'both thesize of the particles and the concentration of diamonds may be varied.The concentration of t-ical spindle of the grinding wheel 18. The base28 of diamonds is normally expressed in'terms of carats per cubic'inchof matrix. A carat is equal to 200 milligrams. The highestdiamond-concentration which is normally available is about 110 caratsper cubic inch; the most commonly used concentration is 72 carats percubic inch.

With regard to grit size, commercial grade diamonds are generallyavailable in gritsizes designated, for example, 50 to 60 grit or 30 to40 grit. The grit size figure tions are less than a few microinches, byapproximately 14 stages of diamond grinding, each correspondinggenerally to the stage shown in FIGS. 1 and 2. With varying widths ofplate glass, it is to be understood that the grinding stations will belarger. or smaller, and that they 7 pass through a 50 mesh screen butwill not pass through will be modified in accordance with known machinetool I practice to provide economical installations for'any widthconclusions, a few'brief paragraphs will be directed to I definingthevariables which are involved and the technical defini-tionsof variousterms which will'be used. i

Some of the basic variables are evident from a con:

isideration of FIGS. 1 and 2. Thus,the conveyor speed for the glasssheet 1 2 isla first obvious variable, and the 9.60 mesh screen. Thereare several standards by which screens are identified; in thepresent'specification the basis for the grit sizes is the US. SieveSeries... In many cases,

the average particle size in terms of its diameter in from the grindingsurface, as well as to carry away the ground glass particles, thegrinding area is flooded with coolant The coolant is conventional andincludes oil and emulsifier which permits the formation of an oil inwater'emul'siom'which serves as .thefcoolant- The term rate of rotationof the diamond grinding wheel 18 is an Z 'other variable. The conveyor.speed or rate of feed of the plate glass sheet 1-2,is normally given interms of inches per minute. The present speed which is used in one knownarrangement is about175 inches 'per minute.

coolant concentration as used in the present specification refers ,tothe volume ratio. of water to the concentrated coolant, including' oiland an emulsifier. The grindingconditionsivary to a, considerable extentwith changes in the coolant concentration. Thus-with lean coolantconcentrations, having a lowproportion of oil, lower a diamond wheellife is usually obtained, while with higher While the present inventionis applicable to lower speeds of advance, it is contemplated thatspeedsof 200 inches per minute orhigher are also practical withthe-inventionproportions of oil, this trend is reversed.

ration may be measuredinterms of cubic inches of mond wheel 18 in termsof revolutions per minute is not 7,

equal to the circumference of thejwheelmultiplied by the number ofrevolutions per unit time of the wheel.

Thus, with'the wheel having a diameter of about 10 feet; I

the rate of rotation is about to revolutions per 7 minute in order; toproduce a relative velocity between the glass and the diamond grindingsurface of about 2800 or 3000 surface feet per minute}, v

The amount of stock removed from the plate glass iS i 'whichisproducedin the glass.

glass removed per. caratof diamond which is used. By a the use of. thediamond grinding conditions described in thepresent specification, awheel life of '2600 or more cubic inches of glass pervcarat may beachieved. f I

Another factor whichis important in evaluating the meritsof a particulartype of. grinding wheel is the stress I 7 Obviously, the chipping orbreakage of glass which results from high stresses cannot be toleratedto any si'gnificant'exte'nt, When diamond particle sizes which are toolarge are employed, it has been found that chipping'or breakage occurs.Similarly, high stresses :are produced by usingexcessively high diamondconcentrations when large amounts ofstock are to be removed at earlystages in the plate glass grinding process. In addition, lean coolantconcentrations are accompamedbyanincrease in the grinding stresses." Thespindle powerjwhich is absorbed is an indication of stress, and thelikelihood of chipping or glass-breakage.

The surface finishes' referrcd to in the present case are saw/e24 interms of the R.M.S. or root mean square average height of the profile ofthe glass, where the height is in terms of the departure from acenterline. Where a series of measurements are taken, the R.M.S. surfacefinish is computed by taking the square root of the sum of the squaresof the heights divided by the number of measurements. This type ofaverage gives greater weight to larger deviations from the centerline,and, in practice, gives values which are about 11 percent higher thanthe arithmetic average. A commercial profilometer is employed for thesemeasurements.

Now that the basic terms employed in the diamond grinding of plate glassand in its evaluation have been defined, an overall process forproducing finished plate glass and one specific process for the diamondgrinding of plate glass will be described. In this regard, it is to beunderstood that the overall process and the diamond grinding sequence ofsteps are illustrative specific processes, and that departures from thespecific matters set forth are contemplated and are to be expected inmany cases.

With reference to FIGS. 3 and 4 of the duawings, FIG. 3 represents aknown plate glass process, and FIG. 4 is a plate glass =finishingprocess which includes diamond grinding steps in accordance with thepresent invention. In FIG. 3 the plate glass is produced in a continuousflat sheet from the melting furnace 36. The rate at which the glass isproduced by the furnace 36 controls the speed of operation of theremaining steps in the finishing process. As mentioned above, this speedranges upwardly from 150 inches per minute; in the case of the prior artsystem of FIG. 3, a speed of 175 inches per minute was employed, and inthe present system of FIG. 4 a speed of 200 inches per minute iscontemplated.

The plate glass from the melting furnace 36 is initially passed throughan annealing chamber 38. From the annealing chamber, the glass issupplied first to the beach sand grinding stations 40 and subsequentlyto the iron oxide, or rouge, polishing stations 42. It may be noted thatthere are 28 beach sand grinding stations and 42 polishing stations,making a total a total of 70 stations. At the end of the polishingstations designated by the block 42, the surface of the glass hassurface variations of less than one microinch R.M.S. on the first side,which has been completed. At the intermediate point between the beachsand grinding stations 40 and the polishing stations 42 the surfacefinish is in the range of 12 to 20 microinches R.M.S.

In some cases the plate glass is cut at the end of the annealing chamber38 prior to passage to the beach sand grinding stations. It is thenblocked or clamped and fed successively through the various grinding andpolishing stations. Alternatively, the glass may be fed directly fromthe annealing chamber through the beach sand grinding and the polishingstations until the physical length of the manufacturing plant requirescutting and transfer of the plate glass sheets.

Following completion of polishing one side of the plate glass in thepolishing stations 42, the plate glass is turned over, blocked andpassed to the second stage processing apparatus including the beach sandgrinding stations 44 and the iron oxide polishing stations 46. Thiscompletes the preparation of both sides of the sheets of plate glass.

In accordance with the present invention, the process shown in FIG. 4also includes a melting furnace 48 and an annealing chamber 49. However,the first side processing includes 14 diamond grinding stationsdesignated 50 and only 21 iron oxide, or rouge, polishing stations 51.Similarly, the second side processing operations include only 35stations, of which 14 stations are the diamond grinding stationsdesignated 52 and 21 stations are the rouge polishing stationsdesignated 54, in FIG. 4. The

surface finish following the diamond grinding stations 50 or 52 is lessthan three micro inches R.M.S.

In comparing the processes of FIGS. 3 and 4, it may be noted that thefourteen diamond grinding stations replace 28 beach sand stations and 21rouge polishing stations, or a total of 49 stations. This is a reductionof more than three to one in this group of stations.

The nature of the grinding operations at each of the 14 stations is setforth in some detail in the following Table I. In this table the amountof stock removed, the grit size of the diamond abrasive, thecorresponding average diamond particle size, and the resultant surfacefinish of the plate glass are specified.

Table I Average Surface Glass Particle Finish Station No. Removal GritSize Size (micro- (inches) (microns) inches- R.M.S.)

The foregoing data are contemplated for use in a plate glass processingscheme in which the glass is 1'20 inches in width, and the conveyorspeed is 200 inches per minute. The total glass removed at the 14stations is equal to about 0.025 inch. Following the rough and finegrinding in the 14 stations, the surface finish will have variationswhich are about 2 to 3 microinches R.M.S. It is further noted that thewheel life for the complete diamond grinding process will be above 2600cubic inches of glass per carat, and will be considerably higher thanthis for some of the grinding stations.

The plots presented in FIG. 5 of the drawings show some interestingfacts about the 14 station grinding systern. In FIG. 5, the glassremoval, the diamond particle size, and the diamond concentration areplotted against various station numbers. Thus, glass removal is shown byplot 56 as extending from a maximum of 0.006 inch of stock removal atthe first station down to 0.0001 inch, or 1/ 10,000 of an inch at thefinal or fourteenth diamond grinding station. The diamond particle sizefor the various stations is also shown by plot 58 in FIG. 5. The glassremoval plot 56 and the particle size plot 58 are of the same generalform, and, as a result of the scales which were selected, overlie eachother at stations 11 through 14.

One interesting feature of plot 58 is the constant particle size for thefirst three stages of diamond grinding. This is a result of testsindicating that larger particle sizes produce undesirably high stressesin the glass, causing edge chipping and cracking of the glass, forexample. In addition, with large diamond particle sizes and therelatively low diamond concentrations which are required, there is anunavoidable variation in the number of active diamonds which are atwork. This factor changes the working properties of the diamond wheel toundesirable extent.

In FIG. 5 the diamond concentration is shown in plot 60 as an increasingcharacteristic. Thus, as the diamond particle size decreases, thediamond concentration increases.

Furthermore, it is desirable that the product of diamond particle sizeand diamond concentration be of the same order of magnitude insuccessive grinding stages. In this regard, it may be noted that atstations No. 1, No. 2 and No. 3, the diamond concentration is about 9carats per cubic inch, and the particle size is about 275 microns,yielding a product of about 2475. At station No. 5 the 7 r 7 averageparticle size is about 137 microns,and the concentration is'2 carats percubic inch; The product of these two figures is 3425. At station No.8'the average particle size is 68 microns, and the concentration isabout 40 carats per cubic inch. The product of average particle size andconcentration produces a product of 2720 in this case. The product ofdiamond concentration 'and V of particle size thus averages at about2900,'and the products for the various stations as calculated above areall within 25 percent of this figure. In general therefore, they are ofthe same-order of magnitude, i.e., none of the products depart from theaverage product by SO-percent or more.

Concerning certain other particulars for .the specific complete systemdescribed above, the coolant concentration is 25 parts of water to onepart of oil, and the grinding speed is approximately 2800 to 3000surface feet per minute. I In order to provide this speed at theperiphery of the 10 foot grinding wheels, the'spindles havea rate ofrotation of approximately 90 to 95 revolutions per minute.

, for the entire 14 stages of the grinding operation. How ever, withdifferent types of commercially available grinding oil and differentsurface finishrequirements, as well'as other; changes in grindingconditions, it is. evident that other coolant concentrations may beemployed. Thus the effect of coolant concentration is an importantfactor in combination with the completegrinding process.

"lGrit size tests V i I In consideringthe'maximum grit size to beemployed for the initial coarse grinding plate glass stages, extensivetests were'madej on the to gritsize wheels. In these tests varyingdiamond concentrations including 4,' 5, 9,

v and 18 carats per cubic inchwere considered. In addi- The foregoingspecific glass grindingsystem and method is the result of studies of agreat amount of test data. "In

the course of the tests, varying amountsof stocks were removed,different coolant concentrations and spindle. speeds'were employed, andgrinding wheels with manydiiferent diamond concentrations and particlesizes were tested under many diverse conditions; In the-followingparagraphs, the significant results of many of these tests will besummarized.

V Grinding speed tests tion, varying speeds, feeds and coolantconcentrations were employed. The maximum wheel life obtained in thesetests was 1800 cubicinches of glass per carat.

1 This, of course, compares quite 'unfavorably with the wheel life of2500 to' 3000cubic inches of glass per carat which is obtainable withto' grit wheels. In addition, with downfeeds of 0.005 inch, selected asthe minimum downfeed of interest for the 20 to 30grit size, high glassstresses; producing glass-breakageand excessive spindle power, wereencountered. Furthermore, throughout the tests with the20 to 30 gritsize, excessive edge chippingof I the plate glass was also encountered.

lnaddition to the extensive tests with relatively large particle sizesto determine the initial diamond cutting V In a series of tests witha'grinding wheel having'grit size of 50 to'60 and a diamondconcentration of 9 carats per cubic inch, the effect of varying thespindle speed was studied. In this test a coolant concentration of 50:1and grinding wheel diameter was three inches.

The results of these tests are'shown in graphical form in FIG. 6. Asshown by this graph, the'wheel life versus a grinding speed curve has abroad maximumextending from slightly above 2,000 surface feet per minuteto slightly above 4,000 surface feet. per minute, withthe maximum wheellife between 2,700 and 3,700 surface feet per minute. Coolantconcentration tests 7 The effect of coolant concentrationon wheel life,surface finish andspindle power was extensively examined. FIG; 7 shows arepresentative set of plots indicating the, increase in wheel'lifewhich; is'obtainedthrough the use of richer coolant concentrations,i.e;,'moreoil for a given amount of water. -The'upper dashed line plotin FIG. 7 is obtained using a downfeed-of 0.0025 inch, while the 'lowerplot represents operating conditions witha downfeed of"0.004 inch.' V

' The tests of FIG. 7 were conducted with a 3 inch diameter metal bondedwheel having a grit size of 50 to 60, and a concentration of 9 caratsper cubic inch. A speed a 'downfeed rate of 0.004 inch were employed;Thecondiions, a large number of tests with intermediate and fine gritsizes and lesser infeeds have been completed. The illustrative detailedexample set forth in Table I and the data included in FIG. 5 indicatethe results of these tests.

Diamond concentration tests A number of tests'have been performed withdiamond wheels having" different concentrations of diamond in terms ofcarats .percubic inch. One typical set of data is shown in F1658. Inthis figure of the drawings, plot 1 62 representsthe wheel life, incubic inches of glass per carat, plotted against diamond concentrationincarats per 1 cubic inch. To provide the data for P168, three wheels ofjust under 3000 surface feet per minute was employed;

Tests were also made using'richerco olant concentrationssuch as 12.5 to"one. The slight additional increasein wheel life wasnot considered tojustify the additional expense of doubling the amount of coolant oil andemul- I I sifier to be employed. 7 H v v I, V

It was also found that thespindle power increased appreciably withincrease in the c'oncentration in the coolant I from 25 parts Water toone part of oil and emulsifier, to

100:1, for example. Increase inthe concentration of a V coolant also hadthe effect .of improvingithe surface finish to some extent. i I Iaddition to the tests made with the particular conditions describedabove, the effect of varying coolant concentration was examined for manyotherdiamond wheels and test conditions. In general, it appears thata'coolant concentration of approximately 25 to one is most'suitablehaving diamond-concentrations of 7.5, 9 and 18'carats per cubic inch,respectively, and all having 50-60 grit size,

, were tested under identical conditions. As, shown in plot peared to beeasier to work with, however, and less hard actingfthan the; 18 caratwheels; Thus, under equivalent grinding conditions, the 9 caratwheelproduces less stress in the glass than the18 carat wheel. The increaseinstress in the glass with increasing diamond concentration is indicatedby "plot 64 in FIG. 8 in which an increase in 'power' from 0.75 to 0.84kilowatts is shown as a result of shifting from the 9 to 18 carat wheel.

1 Anumberof tests of the -120 grit size the -120,

and also of the 200-230 grit size diamond grinding wheels were alsomade, with various diamond concentrations. In

general, the results were favorable, and it is evident that wheel lifeabove theaverage of 2600 cubic inches of glass per carat can beobtainedwith these 'sizes of grit. In the .100- grit size, wheels of 20, 30 and40 carats per cubic inch were tested; and, in the 200-230 grit size,wheels of 30, 50, and 70 carats per cubic inch weretested. As a resultof these grinding tests, and examinations of diamondconcentrations inthe grinding surfaces, indicating departures of the wheels from thenominal diamondconcentrations, it was determined that concentrations ofabout 9 20 to 30 carats per cubic inch are to be preferred for the 100to 120 grit size. Similarly, for the 200 to 230 grit size,concentrations of 30 to 50 carats per cubic inch are to be preferred.

It may also be noted in passing that with fine grit size, diamond wheelalignment becomes increasingly important. When the wheel is not properlyaligned with the work surface, the wheel becomes burnished, and wheellife is reduced.

Diamond grinding wheel construction The details of one specific grindingwheel arrangement will now be disclosed in connection with FIGS. 9through 15 of the drawings. In general, FIGS. 9 and 10 show thesupporting structure and certain diamond grinding segments assembled tothe support, FIGS. 11 and 12 show holders for sets of three of theindividual diamond grinding inserts, and FIGS. 13, 14 and 15 show theindividual diamond grinding inserts in combination with their mounts.

The diamond grinding wheel support 18 shown in FIG. 9 has a centralopening 70 and an outer periphery 72. As clearly shown in FIG. 10 (asectional view diametrically across the grinding wheel of FIG. 9, butupsidedown with relation to its normal operating position wherein thegrinding elements would be positioned above the sheet of plate glassbeing surfaced), individual diamond grinding elements such as thosedesignated 74 and 76 are mounted on one side 78 (normally the lowerside) of the support 18. The other side 80 (normally the upper side) ofthe support is secured in engagement with the vertical spindle of agrinding machine such as those shown in FIGS. 1 and 2 of the drawings.Coolant holes 81 through 84 extend on an outward slant from the upperside 80 to the lower side 78 of the support. When coolant is supplied tothese openings, it flows downwardly and outwardly toward the grindingarea under the diamond grinding segments 74 and 76. In FIG. 10, threediamond segment holders 86, 88 and 120 are shown mounted on the side 78of the support plate 72. These holders 86, 88 and 120 are secured to thesupport plate by the nuts 90, 91 and 92 which engage threaded extensionswhich are centrally attached to the holders 86, 88 and 120'.

The diamond segment holders are shown in greater detail in FIGS. 11 and12. As clearly shown in these figures, each segment holder includes abody portion 94, a centrally extending stud portion 96, and threerecesses 98, 100 and 102. The diamond segment assemblies include a mount104 and a diamond grinding element or segment 106. These assemblies areclearly shown in FIGS. 13, 14 and 15 of the drawing. The diamondgrinding element is bonded to the mount 104 by a bonding material 108.Alternatively, these members may be welded or soldered in position. Thediamond segment assemblies are secured in position by means of setscrews (not shown) which extend through the tapped holes 110, 112 and114 into engagement with the mounts. The countersunk hole 116 as shownin FIGS. 11 and 12 receives a cap screw which engages one of severaltapped holes in the support plate to maintain the segment holders in thedesired angular orientation, as discussed below.

In FIG. 9 a total of five segment holders are shown. These five segmentholders are designated by the reference numerals 86, 88, 12 0, 122 and124. The support plate 18 accommodates a total of 28 segment holders;for convenience in illustration, only five of these are shown in FIG. 9.As shown in FIG. 9, the diamond segments are in various angularorientations. This is accomplished as indicated in FIG. 16 by the use ofa number of tapped holes which may be engaged by the screw passingthrough the opening 116 in the segment holder body 94 mentioned above inthe description of FIGS. 11 and 12. This arrangement is clearlyindicated in FIG. 16 which shows the larger holes 128 and 130 whichreceive the stud portions of two adjacent segment holders. In FIG. 16the additional tapped holes 132 associated with the larger opening 128,and the series of tapped holes 134 for the adjacent stud opening 130,are clearly illustrated. By aligning the opening 116 in the body of asegment holder with the desired tapped hole 132 or 134 as shown in FIG.16, any desired orientation of the segment holders may be obtained.

The diamond segment assemblies may be secured to the sup-port member ofFIG. 9 at desired angular orientations. Thus, they can be aligned withthe periphery of the wheel as shown in the case of the segment holder122; they may be mounted at an angle of 45 with respect to a radial lineas shown by segment holder 88; or they may be oriented at an angle of 30with respect to a radial line as indicated by the segment holders 86,and 124. In some cases, it may be desirable to have all of the segmentsoriented at the angle of 30 as indicated by the three segments 86, 129and 124. In other cases, alternate segment holders may be arranged atdifferent orientations. Other variations to provide desirable grindingcharacteristics may also be provided. It is particularly to beunderstood that any arrangement of the twentyeight diamond segmentholders mounted on the lower side '78 of the support 18 may be employed.Specifically, all twenty-eight of these segments may be mounted withtheir angular orientation the same, at any of the angles permitted bythe angular adjustment holes 132 and 134; or they may be alternated orsequenced with alternate sets of fourteen holders at differentorientations, or with successive holders at four orientations, forexample, so that every fourth holder is at the same orientation.

It may also be noted that the individual diamond segment assemblies maybe rotated with respect to the segment holders. They are then held inposition by the set screws in the tapped holes 110, 112 and 114 as shownin FIG. 11. In FIG. 9 the diamond segments in the wheels 88, 120, 122and 124 are shown aligned with the three openings in the segmentholders. In the case of segment holder 86, however, the diamond segments74 are oriented transverse to the three openings in which the segmentmounts are secured. This additional adjustment provides another degreeof freedom for arranging the diamond segments on the face of the supportmember 18.

The diamond wheel as shown in FIGS. 9 and 10 may, for example, beslightly more than 10 feet in diameter. In this case, the variouselements as shown in FIGS. 9 through 16 would be generally proportionedto this scale. A wheel of this diameter is intended to accommodate plateglass sheets 120 inches wide.

In one specific case, however, the support as shown in FIGS. 9 and 10 is30 inches in diameter. The support has a thickness of 1% inches, and thecentral opening 70 is just under 10 inches in diameter. The segmentholders are just under 3 inches in diameter, and the centers of thesegment holders define a circle having a diameter of approximately 25%inches. The individual diamond segments each have a sun-face area ofapproximately square inch. More specifically, the length of each of thediamond segments, such as that shown at 106 in FIGS. 13 through 15, isapproximately of an inch, and the width is approximately of an inch.

As mentioned above, the support member 18 carries 28 peripherallylocated diamond segment holders, and each segment holder supports threediamond segments. Multiplying the 84 diamond segments by the A squareinch surface area of each segment provides a total surface area ofdiamond matrix of approximately 21 square inches. In accordance with animportant feature of the invention, this surface area is relativelysmall as compared with the total surface area of the grinding wheel. Asmentioned above, the distance between the centers of the diamond segmentholders is slightly more than 25 inches. The average radial location ofthe grinding segments is therefore about 12% inches from the center ofthe grinding wheel. The area of thegrinding'wheel included within thecircle defined by this average radial distance is approximately 490square inches. The 21 square inchfigure of actual diamond grindingsurface is 1 therefore less than 10 percent, and is-even less thanpercent of the 490 square inch surface areaincluded within the circledefined by the average radial locationof the grinding segments. Wheelface width The plots 142 and 144 of FIG. 17 reveal an unexpected effect.This is the pronounced effect of wheel face width on wheel life. Thetests in each caserefer to a 3 inch diameter wheel in which the metalbonded diamond matrix in contact with the plate glass was in the form ofa continuous narrow peripheral area of circular configuration; The wheelface width figures employed for the plots of FIG.- 17 represent'theradial extent of the grinding area. i

The plot 142 in FIG. 17 refers to a 50 to 60 grit wheel cluded in thewheel. 'the high" wheel life and adjustability, and the. fact that wheelin which a continuous diamond surface is employed."

A further advantage of the'arrangement shown in FIGS.

9 and 10 isthe relatively low cost 'of the diamondsin This factor incombination with.

. different types of diamond segments'may be employed a in successivestations with the same type wheel support,

having a diamond concentration of 18 carats per cubic I per cubic inch,and the coolant concentration was parts l of water to one part of oiland emulsifier.

Itis interesting to note that the wheel life, or efficiency, Y

with the optimum wheel face widthis more than-twice the efficiency.obtained with face widths which depart significantly from the optimumwidth. Another factor of interest is the shift in optimum wheel facewidth from approximately 0.24 for the 18 carat pe f ubic inch wheel toapproximately 0.27 for the 9 carat per cubic' 'inch all. indicate theversatility and usefulness of the 0011- struction form shown in FIGS. 9and 10. 1

With regard to the grinding process and apparatus de scribed above, itis contemplated that various alternative arrangements'may be usedx Thus,instead of a single grinding head extending across the entire width ofthe plate glass, two or more grinding wheels having overlapping workareas may be used. I 7

.Similarly', Sinstead'of processing oneside of the plate glass at atime, both sides may be processed simultaneously, lwith grinding wheelslocated abov'eand below the plate glass. v With'this last mentionedarrangement, the '20 glass 'must, of course, be adequately supportedopposite:

the active grinding wheels, and by bearing surfaces toward thei'centerof theu'nderlying grinding wheels.

--It i's'also' noted thatthe stock removal at successive stations isdesigned to minimize the number of stations which are required,consistent with an average wheel life 'of'2600or more cubic inches'ofglass removed per carat.

With higher glass conveyor feed'rates in inches per minute, the processcould be modified by reducing the amount of stock removed at ea'chstation while maintaining the same'iefiiciencyg Similarly, "coolantconcentrations may bemadel'eaner, down to"2 00, 500, or even 1,000.parts of waterto one partof oil, in some cases. .As noted above, thistend's'to increase the stresses inthe plate glass,

- and require reduction in stock removal., Thus, to comwheel. Thus, thewheel face width is dependent on the I concentration of diamonds, andshould be less with higher diamond concentrations. f a

In the course of extensive additional tests, it was foundthat theoptimum points as indicated in FIG. 17 did not shift to anysignificantextent with variations in coolant concentrations. It has alsobeen determined that wheel face width is a significant factor at'othergrit sizes andgrinding conditions. i i

With reference to the construction of the diamond I wheel as shown inFIGS. 9 through l6,'this design is in part a result of the wheelfacewidth'studies discussed above. By changing'the orientation of the28; segment holders mounted on thesupport plate, the effective wheelwidth of the diamond wheel may be changed- Thus,for example, theorientation of the diamond segments in holder 122 provides a relativelynarrow face width, whereas that, of segment holders 88, 120 and 124provides'a broader face width. The effective face width of the wheel 7may also be varied by'rotating the individual diamond segment mounts asdiscussed above. in connection with,

segment holder 86 as shown in FIG. 9.

The segments'at the early stages of grindingjinwhich I goes'down toabout 0.02. cubic inch per minute per inch pensate for higher conveyorrates or leaner coolant con- 'centrations,the depth of. stock removalper stage maybe. reduced and thernumber of stations increased asvcompared with the data of Table I. In the case of the higher conveyorspeeds, approximately the same amount ofglass would be removed perstation; while in the case of the leaner coolant,concentrations; lesseramounts of glass would'be removed .per stationwln each case ofthe dia-'mond wheel life, interms .of cubic inches of glass re- 'movedper'ca'rat,would be approximately'the same. The

advantages of leaner, coolantconcentra'tions include re'-, .ductionin'coolant cost and some; improvement in surface finish; The amount ofglass which is removed'at each station.

' may be expressedas inTable I in terms of the thickness L of the layerof glass which is ground away. Alternatively,

it may beiexp'ressed in terms of'cubic inches of glass removedper minuteper inch of width'ofxgrinding surface.

Thus, with a feed speed'of 200 inches per minute, and stock removal of0.006 inch, the rate of stock removal for Station No. 1; of Table I is1.2 cubic. inches. of glass per minute for each inch of diameter ,ofthegrinding wheel..' In subsequentstations the rate of stock removal fofwidth of grinding surface, atthe last station.

the diamond concentration is relatively low, may be oriented to providea moderately'wid'e face width. vAt

stations further down the grinding line, where the. dia-- mondconcentrations are higher, it may have a reduced f face width. This maybe accomplished using wheelscof the form shown inFIG. 9 by shifting theorientation of either or both the segment holdersand mounts as discussedabove. Also,,if desired for the purposeofmodi fving wheel face width,the segment widths may be varied 7 The diamond grinding wheel of FIGS. 9and 10 is also" from the inch dimension which has been noted above.

designed to usesegments of diamond matrix ratherthan a continuousgrinding surface. I In addition to advantages of adjustabilityasdiscussed above, it has beeirdetermined that a segmented wheel giveslonger wheel life than a Various'advantages ofth'e present inventionhave been discussed above, These include. reduction, in machinery, floorspace material-handlingfacilities and the like. In addition, it ma benoted that thediamond wheels do not require trui'ngor. dressingthroughout their useful life. 7

'Thus','one of the-adverse factors which is often associated withdiamond grindingis notipr esentin the process and system of thisinvention.

4 Another; important ad antage of the; present invention 'isthereIativepurityof the glass particles which are ,re-

moved by diamond'grindin'g This 'is inisharp contrast to the admixtureof sand and glass obtained by the beach' sand grinding ,methodpreviously employed. With reference to FIG." 1 of thedrawings', thecoolant system30 includesconventional arrangements for separating theglass powderfrom the coolant, including filteringand.

settling apparatus, for example. The resultant clean and well definedglass powder is a valuable by-product of the process.

The specific data and the illustrative process described above are basedon commercially available plate glass of the usual type. It is to beunderstood that there are some slight variations in the hardness ofglass; however, this will not affect the results set forth above to anyconsiderable extent. However, in the case of glass or other materialswhich are somewhat harder or softer than the standard plate glass whichis presently available, corresponding changing in grinding feeds andspeeds would be necessary. Thus, for example, harder glass would requirecuts of less depth, smaller conveyor feed rates, or similar changes inthe grinding conditions. Similarly, with softer glass or other material,higher feed rates and speeds and deeper cuts would be practical.

In the present specification and claims the term diamond is widelyemployed. It is to be understood that this term applies both to naturaland synthetic abrasives having the approximate hardness or otherabrasive qualities of diamonds.

It is to be understood that the above described arrangements areillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

1 claim:

1. Apparatus for the continuous surfacing of the principal surfaces of asheet of plate glass and the like, comprising a plurality of grindingstations arranged seriatim in a grinding line, means for advancing thesheet of plate glass successively through each of said plurality ofgrinding stations, each of said grinding stations including a grindingWheel having a generally annular abrasive grinding face of predeterminedeffective radial width with diamond particles bonded therein, saideffective radial width being of a size equal to or less than 0.36 inch,a first one of said plurality of diamond grinding stations having saiddiamond particles in said grinding face in a predeterminedconcentration, a successive one of said plurality of diamond grindingstations having a respectively higher concentration of diamondparticles, the average particle size of said diamond particles in eachof said first and said successive grinding stations being sub- 14stantially within a range of from 275 to 68 microns, and means forintromissively supplying coolant between said grinding face of each ofsaid diamond grinding wheels and the surface of the sheet of plate glassbeing ground thereby.

2. Apparatus for the continuous surfacing of the principal surfaces of acontinuing sheet of plate glass and the like, comprising a plurality ofdiamond grinding stations arranged seriatim in a grinding line, meansfor advancing the sheet of plate glass successively through each of saidplurality of grinding stations, each of said grinding stations includinga grinding wheel having a generally annular abrasive grinding face ofpredetermined effective radial width with diamond particles bondedtherein, said elfective radial width being of a size equal to or lessthan 0.36 inch, successive ones of said plurality of diamond grindingstations respectively having progressively higher concentrations of saiddiamond particles in said grinding face, the average particle size ofsaid diamond particles in each of said first and said successivegrinding stations being substantially within a range of from 275 to 68microns, and means for intromissively supplying coolant between saidgrinding face of each of said diamond grinding wheels and the surface ofthe sheet of plate glass being ground thereby.

3. Apparatus as claimed in claim 2, wherein said average particles sizeof said diamond particles in each of said diamond grinding wheelsprogressively decreases in each successive station with respect to thepreceding diamond grinding station.

4. Apparatus as claimed in claim 2, wherein the respectiveconcentrations of said diamond particles in each of three of saidsuccessive grinding stations are substantially in the order of 9 caratsper cubic inch, 25 carats per cubic inch, and carats per cubic inch.

References Cited by the Examiner UNITED STATES PATENTS 2,198,377 4/40Dunbar et a1 51103.1 X 2,578,789 12/51 Donnelly 51-110 2,945,330 7/60Peyches 51283 X 3,007,288 11/61 Brewin 5111() I. SPENCER OVERHOLSER,Primary Examiner.

FRANK E. BAILEY, Examiner.

2. APPARATUS FOR THE CONTINUOUS SURFACING OF THE PRINCIPAL SURFACES OF ACONTINUING SHEET OF PLATE GLASS AND THE LIKE, COMPRISING A PLURALITY OFDIAMOND GRINDING STATIONS ARRANGED SERIATIM IN A GRINDING LINE, MEANSFOR ADVANCING THE SHEET OF PLATE GLASS SUCCESSIVELY THROUGH EACH OF SAIDPLURALITY OF GRINDING STATIONS, EACH OF SAID GRINDING STATIONS INCLUDINGA GRINDING WHEEL HAVING A GENERALLY ANNULAR ABRASIVE GRINDING FACE OFPREDETERMINED EFFECTIVE RADIAL WIDTH WITH DIAMOND PARTICLES BONDEDTHEREIN, SAID EFFECTIVE RADIAL WIDTH BEING OF A SIZE EQUAL TO OR LESSTHAN 0.36 INCH, SUCCESSIVE ONES OF SAID PLURALITY OF DIAMOND GRINDINGSTATIONS RESPECTIVELY HAVING PROGRESSIVELY HIGHER CONCENTRATIONS OF SAIDDIAMOND PARTICLES IN SAID GRINDING FACE, THE AVERAGE PARTICLE SIZE OFSAID DIAMOND PARTICLES IN EACH OF SAID FIRST AND SAID SUCCESSIVEGRINDING STATIONS BEING SUBSTANTIALLY WITHIN A RANGE OF FROM 275 TO 68MICRONS, AND MEANS FOR INTROMISSIVELY SUPPLYING COOLANT BETWEEN SAIDGRINDING FACE OF EACH OF SAID DIAMOND GRINDING WHEELS AND THE SURFACE OFTHE SHEET OF PLATE GLASS BEING GROUND THEREBY.